Heat pipe condensate return

ABSTRACT

This invention is an improved device for returning the condensate in an evaporation-condensation heat exchanger to the evaporation end utilizing the principle of osmotic action to improve the rate, efficiency and distance of return of the condensed heat exchange fluid.

United States Patent [72] Inventor Stephen C. Baer Albuquerque, N. Mex. [21 1 Appl. No. 838,598 [22] Filed July 2, 1969 [45] Patented Feb. 9, 1971 [73] Assignee Energy Conversion Systems, Inc.

. Albuquerque, N. Mex.

a corporation of New Mexico [54] HEAT'PIPE CONDENSATE RETURN 7 Claims, 3 Drawing Figs. [52] U.S. Cl 165/105, 62/514 j [51] Int. Cl F28d 15/00 mam e 11 Q s h 14 Primary ExaminerAlbert W. Davis, Jr. Attorneys-James E. Snead and William R. Hinds ABSTRACT: This invention is an improved device for retuming the condensate in an evaporation-condensation heat exchanger to the evaporation end utilizing the principle of osmotic action to improve the rate, efficiency and distance of return of the condensed heat exchange fluid.

PATENTED FEB m.

STEPHEN C. BAER INVENTOR ATTORNEY HEAT PIPE CONDENSATE RETURN HEAT EXCHANGER CONDENSATE RETURN This invention relates to a device for improving the return of condensate from the condensation end of an evaporationcondensation heat exchanger to its evaporation end. In particular, the present device incorporates the principle of osmotic action to supply the pumping force to return the condensed heat exchange fluid in an evaporation-condensation heat exchanger to the evaporation end, whereupon the heat exchange cycle is repeated.

Evaporation-condensation principles are well known in the heat exchange art. Many different devices exist for transferring the heat exchange fluid both in its vaporized form from the evaporation end or the heat source end of the heat exchanger to the condensation or heat rejection end, and for return of the condensate to the heat source for repetition of the heat exchange cycle. Heat pipes are an example of one of the many different types of devices for accomplishing this type of heat exchange. A heat pipe generally consistsof a sealed container having a certain amount of working fluid contained therein with one end of the container being exposed to the heat source. The application of heat to the fluid causes it to evaporate. The vapor travels through a passage within the heat pipe to its cooler end where the heat is rejected and the fluid condensed. In heat pipes the condensate is returned to the heat source or vaporization end through the capillary action of a wick. The surface tension of the condensate within the wick provides the pumping action for the return of the condensate.

Evaporation-condensation heat exchangers have in the past been somewhat limited in their use, and one of the major limitations is that the capillary condensate return system is a 'very weak pump. The capillary action is only able to lift the condensatea distance of between I and 4 feet depending upon the fineness of the wick and the type of working fluid contained in the system. The pumping action is further limited by various acceleration forces to which a particular heat exchange system is subjected in use, to its particular position with relation to the force of gravity and to the size of the return passage for the condensate.

It is therefore an object of this invention to provide an improved condensate return system for evaporation-condensation heat exchangers.

A further object of this invention is to provide an improved condensate return system for evaporation-condensation heat exchangers wherein the return of the condensate to the heat source is not materially affected by the force of gravity or by other external forces exerted on the heat exchange system.

A further object of this invention is to provide an improved condensate return system for evaporation-condensation heat exchangers which increases the power and elfiiciency of return of the condensate from the condensation end of the heat exchanger to its evaporation end by utilizing the principle of osmotic transfer of liquids.

A further object of this invention is to provide an improved condensate return system in an evaporation-condensation heat exchange system wherein a semipenneable membrane is interposed between the liquid-vapor interface to supply an osmotic pumping action to the condensate return system.

A further object of this invention is to provide an improved condensate return system which may be used singly or in conjunction with a wick condensate return.

Other objects and advantages of this invention will become apparent as the same is better understood by reference to the following specification and the accompanying drawings.

Referring to the drawings:

FIG. 1 'is a cross-sectional view of one embodiment of this invention showing a semipermeable membrane interposed at the vapor-liquid interface in a heat pipe.

FIG. 2 is a cross-sectional view of a second embodiment of the invention showing a second heat pipe with a semipermeable membrane interposed at the vapor-liquid interface.

FIG. 3 is a cross-sectional view of a third embodiment of this invention wherein a semipermeable membrane forms one side of the vapor passage.

Reference will now be made to the drawings wherein like numbers represent like parts. It should be specifically understood herein that the present invention is not limited to the specific embodiments thereof shown in FIGS. 1, 2, and 3. There are many various types of evaporation-condensation heat exchangers, some utilizing the heat pipe principle and others utilizing difierent heat exchange principles. Basically, the improvement disclosed herein could be used in any heat pipe type heat exchanger requiring pumping action to return the condensate from the heat rejection end of the heat pipe to the working liquid reservoir. I

This invention comprises a sealed container I0 having a solution return channel ll formed in the interior thereof which contains a predetermined amount of working solution such as sugar and water or some other suitable heat transfer solution. The hollow interior 14 of the sealed container 10 forms a vapor passage. One end 12 of return channel II is designed to be the condensation end of the container l0, and the other end 13 is the evaporation end. being exposed to a heat source.

To facilitate passage of the vapor into solution in return channel 11 and to supply the pumping action for return channel ll a semipermeable membrane, such as cellulose, 15 is interposed at the liquid-vapor interface. As shown in FIGS. I and 2 a wick 16 may be inserted into return channel 11 to complement the osmotic pumping action, or it may be omitted as shown in FIG. 3. Moreover, as shown in FIG. 3 theentire return channel may be formed of semipermeable membrane 15, or it can be positioned only at the bottom of vapor passage 14. Return channel 11 in FIG. 3 could be supplied with a wick as shown in FIGS. 1 and 2 if desired.

In the embodiment shown in FIG. 3 the osmotic pumping action occurs along the entire surface of return channel II, and this modification could be added to the embodiments shown in FIGS. 1 and 2. Conversely, the membrane in FIG. 3 could be limited to the bottom of vapor passage 1 1 if desired. Where the entire return channel 11 is formed of membrane 15 it may be desirable to provide periodic openings in the membrane to expedite passage of solvent to solution and solution to solvent.

A seal 17 is provided on return channel 11 in the embodiment shown in FIG. 3 to prevent contamination of the solvent in vapor passage 14 by the solution. Seal I7 is particularly important in applications where wick 16 has been omitted, but can be used in conjunction with the wick.

The operation of this invention is the same in all three embodiments. End 13 having a working solution contained in channel 11 is exposed to a heat source. Application of heat to the working solution causes its evaporation to a pure solvent which enters vapor passage 14 either from wick 16 in FIGS. 1 and 2 or through seal 17 or the sides 15 of return channel II in FIG. 3. In the embodiment shown in FIG. 3, seal 17 could be eliminated and periodic openings could be provided in membrane 15 to expedite passage of solvent into vapor passage 14. The vaporized solvent is conducted by vapor passage 14 to condensation end 12 of container 10 where the relatively cooler temperature condenses the vapor onto semipermeable membrane 15 causing it to give up its latent heat of vaporization through the walls of container 10. The pure liquid solvent then passes through semipermeable membrane 15 into solution in return channel ll.

As is well known, the passage of the solvent through semipermeable membrane 15 into solution creates an osmotic or pumping pressure considerably stronger than the usual capillary action caused by the surface tension of the fluid. The pressure is also considerably above the hydrostatic head of the solution in return channel 11 and does not depend on the position of sealed container 10 nor is it materially affected by gravitational or acceleration forces acting on the fluid.

working solution contained within said solution return The osmotic pressure in return channel ll combined with the capillary action of wick 16 in FIGS. 1 and 2. and independently in FIG. 3 forces the solution through return channel 11 to end 13 of container where the evaporation-condensation cycle is repeated.

' r 5 The osmotic force creates a terrific pumping pressure in the condensate return system. This pressure makes the heat pipe independent of gravitational or acceleration forces and considerably broadens the scope of application of the evaporation-condensation heat exchange principle.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the attached claims, the invention may be practiced otherwise than as specifically described.

1 claim:

V1. in an improved heat exchanger condensate return the combination comprising:

a hermetically sealed container made of heat conducting material and having a heat receiving and a heat rejecting end;

a solution return channel formed within the interior of said hollow sealed member which channel has one wall formed of the interior of the walls of said sealed member;

channel;

a vapor passage within said hollow sealed member and connecting said solution return channel to the heat rejecting end of said sealed member;

said sealed member in oppose between said vapor passage and said solution return channel so that vapor condensed in said vapor passage at said heat rejecting end of said sealed member passes into said solution return channel by osmosis; and

whereby a pumping force is applied to said solution return channel to force the solution within said solution. return channel to the heat receiving end of said sealed member.

2. The invention as defined in claim 1 wherein the interior wall of said solution return channel is formed of the semipermeable membrane and the exterior wall is formed of said sealed container.

3. The invention as defined in claim 2 wherein the top of said solution return channel adjacent to the heat receiving end of said sealed member is open.

4. The invention as defined in claim 2 wherein the top of said solution return channel is sealed by said semipermeable membrane.

5. The invention as defined in claim 2 wherein said semipermeable membrane has openings spaced about its periphery to facilitate passage of solvent therethrough.

6. The invention as defined in claim 1 including wick means within said solution return channel to complement the osmotic action of said semipermeable membrane in returning the solution from the heat rejecting end of said sealed container to the heat receiving end.

7. The invention as defined in claim 6 wherein said semipermeable membrane forms the interior wall of said solution return passage and the walls of said sealed member provide the exterior surface of said solution return channel. 

1. In an improved heat exchanger condensate return the combination comprising: a hermetically sealed container made of heat conducting material and having a heat receiving and a heat rejecting end; a solution return channel formed within the interior of said hollow sealed member which channel has one wall formed of the interior of the walls of said sealed member; working solution contained within said solution return channel; a vapor passage within said hollow sealed member and connecting said solution return channel to the heat rejecting end of said sealed member; a semipermeable membrane in said heat rejecting end of said sealed member in oppose between said vapor passage and said solution return channel so that vapor condensed in said vapor passage at said heat rejecting end of said sealed member passes into said solution return channel by osmosis; and whereby a pumping force is applied to said solution return channel to force the solution within said solution return channel to the heat receiving end of said sealed member.
 2. The invention as defined in claim 1 wherein the interior wall of said solution return channel is formed of the semipermeable membrane and the exterior wall is formed of said sealed container.
 3. The invention as defined in claim 2 wherein the top of said solution return channel adjacent to the heat receiving end of said sealed member is open.
 4. The invention as defined in claim 2 wherein the top of said solution return channel is sealed by said semipermeable membrane.
 5. The invention as defined in claim 2 wherein said semipermeable membrane has openings spaced about its periphery to facilitate passage of solvent therethrough.
 6. The invention as defined in claim 1 including wick means within said solution return channel to complement the osmotic action of said semipermeable membrane in returning the solution from the heat rejecting end of said sealed container to the heat receiving end.
 7. The invention as defined in claim 6 wherein said semipermeable membrane forms the interior wall of said solution return passage and the walls of said sealed member provide the exterior surface of said solution return channel. 